Why do I need to use my new LT IBAN when my GB IBAN will work until end-September?

We anticipate that after Brexit, European banks will impose additional charges on payments to 'GB' IBANs. If you keep using your 'GB' IBAN after December 31st 2020, this could mean that you will receive less than the amount originally sent. However, by using your new 'LT' IBAN you will avoid any such fees imposed by European banks.